We took our first look at the STS- V a year ago ( C/D,February 2005), and it generated positive anticipation on a couple fronts. For one, it figured to provide a more refined level of all-around performance than the Corvette-engined CTS- V, which, for all its visceral appeal, is more hot rod than luxury sports sedan. Second, when judged by the prototype shown at the 2005 Detroit show, the STS- V looked to be the most appealing manifestation yet of Cadillac's knife-edged-design direction. Beyond that, we knew the car's dynamic development would be conducted under the baton of John Heinricy, GM's director of high-performance vehicle operations. With nine Sports Car Club of America national championships in his racing log book, Heinricy definitely knows how to summon haste from a given package, and we anticipated something more stimulating than the other STS variants. The question was how far Heinricy would be able to go on the aggression meter.

Visible variations from the standard STS include a lower front fascia with three air intakes, one for increased airflow, the outer two for increased brake cooling; wire mesh grilles; deeper rocker panels; a lower rear fascia with a mesh-grilled vent at its bottom edge; and a slightly higher spoiler that's been moved rearward at the trailing edge of the decklid. The car has a pronounced forward rake, and the net of the various changes is reduced high-speed lift, as well as a more determined appearance.

High speed is definitely part of this Caddy's act. Last February we forecast 440 horsepower and 430 pound-feet of torque for the 4.4-liter supercharged V version of the car's DOHC 32-valve Northstar V-8. Turns out those numbers were conservative. Fed by a Roots-type blower, the V-8 is rated for 469 horsepower at 6400 rpm and 439 pound-feet of torque at 3800. That's more than 100 horsepower per liter, and it's also the most powerful Cadillac production engine ever offered.

The supercharged eight is mated to GM's new six-speed automatic transmission, typically GM smooth and enhanced by a manumatic function operable with the shift lever (there are no steering-wheel paddles). Suspension tuning is about 15 percent stiffer than that of a standard STS, thanks to Sachs shocks and bigger front and rear anti-roll bars; the variable-assist power rack-and-pinion steering is a bit quicker; and the StabiliTrak system can be programmed three ways: normal, sport, and competitive. In the latter, the car will wag its tail, and power oversteer is readily achievable, something to keep in mind when applying throttle at corner exits.

Inside, the STS- V is richly appointed with enough leather to clothe a small herd of Black Angus — hides on the door panels and dashboard, as well as the seats. The latter have suede inserts to help keep occupants centered in hard cornering, although more bolstering would help. Cadillac enlisted Dräxlmaier for the V's interior décor. The same outfit did the Maybach, and if the Caddy has no granite trim option, it does have olive-stained ash. The whole package is tasteful, roomy, and arguably the most comfortable in this threesome, thanks to the relatively creamy ride and best control layout of the bunch.

This brings us to dynamics, which is where the Cadillac drew reviews that were essentially average for this exalted group. For example, the STS- V's 4.6-second 0-to-60-mph run was slowest in this group, but how many luxo sedans are capable of 60 mph in less than five seconds? Similarly, stopping to a standstill from 70 mph in 170 feet was third-best here, but still exemplary for this weight class.

Where the Caddy fared worst was in Grattan's twists and turns. Although the steering was quick and nicely weighted, excessive up-and-down motion in the suspension inhibited transient responses, and observers noted substantial brake dive compared with the German cars.

On the other hand, the STS- V's price nets you a no-apologies supersedan with big money left over — almost 16 large versus the CLS55. That's a huge advantage — especially since the STS- V has this group's most comprehensive allocation of features and amenities. It's enough, in fact, for the Caddy to edge the Mercedes for runner-up honors.